1. Field of the Invention
This invention relates to an image sensing device with a wide substantial dynamic range.
2. Description of the Related Art
Image sensing devices are being widely used, for example, as the video camera sections of video tape recorders with integrated cameras or as still video cameras. A video camera using an image pick-up tube or a solid image sensing element has a relatively narrow dynamic range as compared with the conventional silver halide photography system, so that it is subject to generation of white blankings and blackenings (common names for portions with excessively high or low luminance) under back light conditions. In conventional video cameras, adjustment of the quantity of light in such cases is effected by opening the diaphragm two steps or so, either manually or with a backlighting compensation button.
However, even when such backlighting compensation is appropriately conducted, with the main subject being properly exposed, white blankings may be generated in the background, leaving the picture with a blank background. In other words, the narrowness of the dynamic range in an image sensing device cannot be overcome merely by adjusting the quantity of light to attain a proper exposure for the main subject, as in the case of conventional devices. To cope with this, an improvement has been proposed in the conventional image sensing device of the type in which a still image is transduced into an electrical signal by means of a line scanner or the like. According to this improvement, a plurality of images of different exposures obtained from the same subject are combined to compose a single picture. Similar ideas are disclosed, for example, in U.S. Pat. No. 4,647,975 and Japanese Laid-Open Patent Application No. Sho 61-219270.
However, they are directed to still images and are not capable of providing a moving picture with a wide dynamic range.